Now that medical marijuana is permitted in about one-third of the nation, advocates hope to move beyond therapeutic uses with ballot questions in three states that could legalize pot for recreational use. Voters in Colorado, Washington state and Oregon face proposals to change state laws to permit possession and regulate the sale of marijuana — though the plant with psychoactive properties remains an illegal substance under federal law. Approval in even one state would be a dramatic step that most likely would face legal challenges but could also bring pressure on the federal government to consider modifying the national prohibition on marijuana that has been in place since 1937, backers say.

“One of these states crossing that Rubicon will immediately set up a challenge to the federal government,” says Allen St. Pierre, executive director of the National Organization for the Reform of Marijuana Laws. Independent polls have shown proponents leading in Washington and Colorado a month or more before the election, but the outcome remains in doubt, and both sides are aware of what happened in California in 2010: The similar Proposition 19 lost 53.5% to 46.5% after an early lead in favor disappeared. “It’s a similar trajectory here,” says Laura Chapin, spokeswoman for a group opposing Colorado’s Amendment 64, who predicts the proposal will be defeated.

John Matsusaka, a professor of law and business who is president of the Initiative & Referendum Institute at the University of Southern California, says the ballot questions on recreational use reflect growing acceptance of marijuana. A Gallup poll in October 2011 showed support for legalization of marijuana at 50%, the highest since Gallup began asking the question in 1970, and 46% opposed. Seventeen states have permitted marijuana use and possession for medical reasons since 1996, when California became the first, and many cities have instructed police to make pot a low priority for enforcement. “Public opinion is trending in this direction,” Matsusaka says. “It’s a matter of time before one of these passes.”

Medical-marijuana proposals are on the ballot in three states: Arkansas, Massachusetts and Montana. The ballot issues arise as the conflict between the federal ban and more permissive states has been growing. Use of marijuana for medical purposes is legal in Washington, D.C., and 17 states: Alaska, Arizona, California, Connecticut, Colorado, Delaware, Hawaii, Maine, Michigan, Montana, Nevada, New Jersey, New Mexico, Oregon, Rhode Island, Washington and Vermont

In California, federal prosecutors have been shutting down medical-marijuana dispensaries, sometimes threatening landlords with asset forfeiture for leasing space to pot shops. Yet federal prosecutors typically do not go after cases of simple possession of small quantities. In Washington state, former federal prosecutors and law enforcement officials are among the supporters of legalization. Campaigns have been intense in Washington and Colorado. In Oregon, St. Pierre says, marijuana advocates are less hopeful and support is not as well-financed.

Former Seattle police chief Norm Stamper, who supports Washington’s Initiative 502, says some police and prosecutors have grown frustrated at the futility of marijuana prohibition and see regulation by states as a way to take the trade out of the hands of criminals and free up the justice system to focus on more serious matters. “They’ve seen the enormous costs associated with marijuana prohibition, and they’ve concluded there ought to be a better way,” Stamper says. “None of us is advocating marijuana use.”

In Washington state, the issue is being sold as a chance to license, regulate and tax marijuana and impose a tough legal standard banning driving a vehicle while impaired by marijuana. Backers added the drugged-driving provision after seeing opponents of California’s proposition two years ago attack it for failing to address driving after smoking or otherwise ingesting pot. Colorado’s proposal would authorize state-licensed production and retail facilities but leave it to lawmakers to follow up with any driving restrictions, says Mason Tvert, co-director of a group pushing the amendment.

New Approach Washington is airing $2 million worth of TV ads in favor of Initiative 502, campaign director Alison Holcomb says. Among them are ads featuring endorsements from two former U.S. attorneys from the Bush and Clinton administrations and a former Seattle FBI chief. “We know firsthand that decades of marijuana arrests have failed to reduce use, and the drug cartels are pocketing all the profits,” Charlie Mandigo, former special agent in charge of the FBI in Seattle, says in one ad. “If 502 passes, we will have more resources to go after violent crimes,” John McKay, former U.S. attorney for western Washington from 2001 to 2007, says in another.

In Colorado, Chapin’s opposition group, Vote No on 64, has no TV ads. It touts opposition to the measure by Democratic Gov. John Hickenlooper, Denver Mayor Michael Hancock, area teachers, ministers and law enforcement groups. In Washington, the opposition group No on I-502 is led by Steve Sarich, a medical-marijuana entrepreneur, who calls the legalization initiative “a Trojan horse” for the strict anti-drugged-driving provision. “There’s a new plan for prohibition in this country,” Sarich says. “The government knows they’re losing the battle, with more medical-marijuana states … so their new strategy, a deviously brilliant one, is ‘You can have your pot — but we’re going to arrest you now for drugged driving.’ ”

Holcomb, who directs the campaign in support of the initiative, laughs off Sarich’s charge and says the provision was added because “Washington state voters, just like voters around the country, are very concerned about impaired driving.” She says approval of the legalization initiative would demonstrate to the federal government that, as in the repeal of the prohibition on alcohol in the early 20th century, the public is ready for change. “This is one of those issues that has to percolate up from the states,” she says. “Congress and the administration need to see that the will of voters has shifted and we are ready to try something different.”